Recent Advances in Covalent Organic Framework-Based Nanosystems for Bioimaging and Therapeutic Applications

Nanomedicine has had potential implications in bioimaging and cancer treatment in the past decade. Nanoscale covalent organic frameworks (COFs) have been developing as a significant category of biomedical nanomaterials with good application prospects on account of their high porosity, functionality, and biocompatibility. The high porosity of COFs permits the encapsulation of distinctive imaging and/or therapeutic agents with high loading efficiency. In some cases, organic building blocks can be employed to load therapeutic drugs and/or functional species through covalent bonding. The organic building blocks of COFs can also be post-modified for specific binding to biomarkers. The unique characteristics of COFs make them promising nanocarriers for bioimaging and therapeutic applications. Despite energetic research on the rational design and fabrication of COFs having been conducted for nearly a decade, the therapeutic applications of nanoscale COFs still remain less understood. This review mainly summarizes the recent research advances in the COF design and their applications in the biomedical field. In particular, the bioimaging and therapeutic applications of COFs are discussed, which include fluorescence bioimaging and different treatment approaches containing chemotherapy, photodynamic therapy, photothermal therapy, and synergistic therapy. The review also illustrates the fundamental challenges facing COF-based nanosystems in terms of size control, surface modification, biodistribution, toxicity, and biocompatibility. This review aims to promote multidisciplinary research at the interface of COFs and biomedicine.